I don't even require "native" in the sense of a look and feel identical to that of the platform-specific GUI framework provided by the vendor of that platform…

I don't even require "native" in the sense of a look and feel identical to that of the platform-specific GUI framework provided by the vendor of that platform… that would indeed be an additional layer of difficulty for a cross platform framework… and the degree to which the different cross-platform toolkits with an own rendering manage to mimick it is quite variable. But I don't even need that. I'm fine with the widgets/UIs of my applications having their own styling that, while (apart from my own special widgets) staying close enough to be understandable by everyone, don't totally closely match the exact current style / "look&feel" of the apps of the platform vendors. What I did mean with "native" in my last comment was simpler than that: I just meant "native" as in: not a web app or similar detached via abstraction layers and bundled with a browser that interprets it, but a natively compiled app that is directly linked to the rendering GUI lib. That would even be enough for me. But even for that, I find there isn't a satisfying cross-platform solution.